diff --git a/substrate/wasm-runtime/polkadot/src/joiner.rs b/substrate/wasm-runtime/polkadot/src/joiner.rs
new file mode 100644
index 0000000000..99b38dec57
--- /dev/null
+++ b/substrate/wasm-runtime/polkadot/src/joiner.rs
@@ -0,0 +1,12 @@
+use slicable::Slicable;
+
+pub trait Joiner {
+	fn join<T: Slicable + Sized>(self, value: &T) -> Self;
+}
+
+impl Joiner for Vec<u8> {
+	fn join<T: Slicable + Sized>(mut self, value: &T) -> Vec<u8> {
+		value.as_slice_then(|s| self.extend_from_slice(s));
+		self
+	}
+}
diff --git a/substrate/wasm-runtime/polkadot/src/lib.rs b/substrate/wasm-runtime/polkadot/src/lib.rs
index e64a3c2a6b..5646c7c322 100644
--- a/substrate/wasm-runtime/polkadot/src/lib.rs
+++ b/substrate/wasm-runtime/polkadot/src/lib.rs
@@ -6,6 +6,7 @@ extern crate runtime_support;
 
 mod endiansensitive;
 mod streamreader;
+mod joiner;
 mod slicable;
 mod primitives;
 mod keyedvec;
diff --git a/substrate/wasm-runtime/polkadot/src/primitives.rs b/substrate/wasm-runtime/polkadot/src/primitives.rs
index a689eb7dce..44d3bc4739 100644
--- a/substrate/wasm-runtime/polkadot/src/primitives.rs
+++ b/substrate/wasm-runtime/polkadot/src/primitives.rs
@@ -1,4 +1,5 @@
-use streamreader::{StreamReader, Joiner};
+use streamreader::StreamReader;
+use joiner::Joiner;
 use slicable::{Slicable, NonTrivialSlicable};
 use function::Function;
 use runtime_support::size_of;
@@ -170,7 +171,7 @@ impl Slicable for Block {
 #[cfg(test)]
 mod tests {
 	use super::*;
-	use streamreader::Joiner;
+	use joiner::Joiner;
 	use function::Function;
 
 	#[test]
diff --git a/substrate/wasm-runtime/polkadot/src/slicable.rs b/substrate/wasm-runtime/polkadot/src/slicable.rs
index 0459881f0e..e220eb0f7d 100644
--- a/substrate/wasm-runtime/polkadot/src/slicable.rs
+++ b/substrate/wasm-runtime/polkadot/src/slicable.rs
@@ -1,5 +1,5 @@
 use runtime_support::{Vec, size_of, transmute, uninitialized, slice};
-use streamreader::Joiner;
+use joiner::Joiner;
 use endiansensitive::EndianSensitive;
 
 /// Trait that allows zero-copy read/write of value-references to/from slices in LE format.
diff --git a/substrate/wasm-runtime/polkadot/src/streamreader.rs b/substrate/wasm-runtime/polkadot/src/streamreader.rs
index 3bb427a1ef..33d6fd8bfd 100644
--- a/substrate/wasm-runtime/polkadot/src/streamreader.rs
+++ b/substrate/wasm-runtime/polkadot/src/streamreader.rs
@@ -20,17 +20,6 @@ impl<'a> StreamReader<'a> {
 		Slicable::from_slice(slice)
 	}
 }
-
-pub trait Joiner {
-	fn join<T: Slicable + Sized>(self, value: &T) -> Self;
-}
-
-impl Joiner for Vec<u8> {
-	fn join<T: Slicable + Sized>(mut self, value: &T) -> Vec<u8> {
-		value.as_slice_then(|s| self.extend_from_slice(s));
-		self
-	}
-}
 /*
 // Not in use yet
 // TODO: introduce fn size_will_be(&self) -> usize; to Slicable trait and implement
diff --git a/substrate/wasm-runtime/polkadot/src/system.rs b/substrate/wasm-runtime/polkadot/src/system.rs
index 96169d09cc..88414fa9a1 100644
--- a/substrate/wasm-runtime/polkadot/src/system.rs
+++ b/substrate/wasm-runtime/polkadot/src/system.rs
@@ -74,7 +74,7 @@ pub fn set_code(new: &[u8]) {
 
 #[cfg(test)]
 mod tests {
-	use streamreader::Joiner;
+	use joiner::Joiner;
 	use function::Function;
 	use std::collections::HashMap;
 	use runtime_support::{NoError, with_externalities, Externalities};